Battle of the Scanners: MRI vs. CT

Imaging techniques operated by skilled professionals has revolutionized the way we diagnose almost all major types of medical abnormalities and illnesses, from chronic conditions to neurological disorders to advanced cancers.

Computed tomography (CTs) and magnetic resonance imaging (MRIs) are some of the most commonly used diagnostic imaging tools. Almost 80 million CT scans, and an additional 80 million MRI scans are performed in the United States annually¹.

If your doctor has recommended either a CT or an MRI, it’s best to understand each method and each tool’s advantages and disadvantages as laid out more fully below.

CTs: What, When and Why

How does a CT work? Essentially, it is a conglomeration of x-ray images produced from different angles which are eventually processed by computers to create tomographic images. This computer-based technology has been greatly improved, developing reconstructed images with high resolution.

CT scans are less constricting than MRIs. They are shaped like a large doughnut standing on its side and the patient lies on a narrow table with a motor that slides through the center of the scanner into a tunnel.

CT scans can be done without dye or with dye contrast, the latter of which can show more detail. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are types of CT scans.

If your doctor has ordered a CT scan, it’s because they are effective techniques for monitoring cancer of the bladder, kidneys, skeleton, neck, and head. The tool can identify distant metastases in the lungs, skeleton, liver, and brain. It can also detect modifications in tumor masses during treatment, for example, gastroenterologists mostly use CTs for the analysis of the liver or pancreas². Another major application of CT scans is the detection of heart diseases like myocardial disease, congenital heart disease, and coronary artery bypass grafts.

CT Advantages:

One of the advantages of CTs is time. From the time you receive a referral for a CT to the time of the examination is generally short. CTs take less time to perform and are more readily available than MRI scans, which means you are more likely to get a quick appointment. From a diagnostic perspective, they are better than MRIs for macrostructure and microstructure of the bone. For those who have feelings of claustrophobia in tight spaces, CTs are easier to handle since they are open devices.

CT Disadvantages:

Physicians are aware that, from a diagnostic perspective, a big drawback of CT scans is that large masses within the gastrointestinal tract may not be visible during an abdominal scan, and there is no finding of some of the mucosal abnormalities³.

From a radiation standpoint, CTs have more ionized radiation than MRIs since they use x-ray technology. The low doses of radiation have not been shown to cause long-term harm, but for repeated scans, there may be a small increase in the lifetime risk of cancer. This can affect children and pregnant women more than others⁴, and might explain why a doctor did not prescribe a CT in those circumstances.

MRI: What, When and Why

An MRI is a large cavernous machine with multiple components, including a slab for patients to lie on, a superconducting magnet, a protective cage, the operator’s console, and computers to analyze the data and produce images. During the scanning process, the machine’s magnet produces a strong magnetic field with radiofrequency waves. A microphone is present inside the MRI unit for communication between the patient and the technologist during the scan.

Like CTs, MRIs can be done with or without contrast dye. MRI technology includes functional MRIs, magnetic resonance angiography (MRA), susceptibility-weighted, diffusion-weighted (PWI), and diffusion-weighted (DWI) imaging.

Physicians will often refer you to an MRI because they are superior for soft tissue examination, for example the white and gray matter structure of the brain or breast tissue. The most common detections by MRI are multiple sclerosis, central nervous system tumors, brain and spine infections, stroke, injuries in ligaments and tendons, muscle degradation, bone tumor, occlusion of blood vessels, and breast cancer. MRI scans can also show cardiovascular functional activities, metabolism, and blood flow in the heart⁵.

MRI Advantages:

From a diagnostic standpoint, MRI scans are better for soft tissue contrast and resolution. The technician and radiologist can also see many planes of the tissue to allow for multiple views from different angles. Because of these multiple views, the degree to which a lesion or abnormal tissue stands out from the surrounding healthy tissue is more easily detectable⁶.

From a physician’s procedural standpoint, MRIs can be combined with other imaging like ultrasounds, PET scans, biopsies, or a variety of scoping technologies. Technicians can also re-image the same section in real time, while the patient is inside the machine and without adjustment⁷.

MRI Disadvantages:

MRIs are very expensive to run and they are time-consuming which means that wait times are longer. Because they are expensive pieces of equipment, they require very specific training and are they sometimes not available in rural areas.

From a patient standpoint, patients with metal implants of any kind can suffer tissue overheating from the radiofrequency waves and it can be quite uncomfortable. MRIs can also be very noisy and can create a suffocating environment those with a tendency toward claustrophobia.

The Key Differences:

The key differences between CT and MRI scans relate to the type of technology used, the availability, and radiation exposure.

CTs uses x-rays and computer technology to produce images while MRIs use magnetic fields and radio waves without ionizing radiation.

CT scans can generally be secured faster and are more widely available, making it the preferred choice in emergency situations. MRIs take longer to perform and may be less available in certain settings, but provides superior detail for soft tissues.

Finally, CTs involve exposure to ionizing radiation, which can be considered less safe than MRIs which use which may be a consideration for certain patients, like pregnant women and young children.

Which One Is Right For You?

The short answer is – your doctor will know and it will largely depend on his or her evaluation of the need. Both are invaluable tools in modern medicine. CTs are preferred for quickly diagnosing acute conditions while MRIs excel in imaging soft tissues.

Your doctor and your insurer will likely consider the specific clinical scenario, the area of the body being examined, and the type of information required.

Second Opinion on Interpreting Scan Results:

Obtaining a second opinion on the interpretation of CT or MRI scan results can be crucial for ensuring a thorough and detailed understanding of your diagnosis. Radiologists may have different perspectives or notice subtle details that could impact your treatment approach. A second review of your scans might reveal additional findings or provide alternative interpretations that could potentially lead to a more nuanced understanding of your condition. This process not only enhances the reliability of the diagnosis but also offers reassurance and additional options for management. Consulting with a second radiology expert might be particularly beneficial for complex cases, rare conditions, or when the initial findings are inconclusive or raise questions. Ultimately, this step may provide you with greater peace of mind and confidence in your diagnostic journey.